The production of solid, powdery Rare Earth carboxylates with branched long- chain ligands, (e.g. Rare Earth 2-ethylhexanoate, versatate, neodecanoate or naphthenate) by conventional methods, produces oily, sticky wax-like materials which upon drying (at from about 60 to about 90.degree. C.) are difficult to convert into powdery materials. One reason for this may be the branched structure of these ligands. The two carboxylic acids which are less prone to give powdery solids, versatic and neodecanoic acid, consist of mixtures of neodecanoic acid isomers in addition to their branched nature. Naphthenic acids consist of monocarboxylic acids of different molecular weight and may contain a variety of hydrocarbon impurities. 2-Ethylhexanoic acid (octoic acid) is available in isomer-free form.
Another reason for the sticky consistency may be the fact that during the formation of these materials various impurities remain incorporated into the product and may be difficult to remove by the usual purification steps. Especially, salts such as nitrates, chlorides, sulfates and the like can be trapped in the product if the method does not offer an easy way to extract these salts. In addition, if the solvent medium consists of polar solvents, such as water, or of alcohols, such as methanol or ethanol, or of ethers, such as THF or DME, the final product can also be contaminated with these. One additional source of impurity is the so-called "free acid", which will be present in the product if part of the carboxylic acid starting material remains unreacted. The presence of free acid can prevent formation of powdery materials. For instance, cerium.sup.4+ octoate is a solid, but in the presence of one molar equivalent of free acid the product is an oil. Because of the complexity of the structure of the final product, even if the theoretical stoichiometry of the reaction does not allow the formation of unreacted acids, the end product may possess a percentage of unreacted acid present.
In other cases, where, instead of powdery materials, stable solutions of Rare Earth carboxylates are of interest, the above mentioned impurities, such as water or free acid, have been discovered to be welcome additives, since they tend to coordinate to the Rare Earth metal and enable the molecule to stay in solution and thus prevent the formation of structurally more sophisticated systems which in turn can precipitate out as waxy materials or viscous oils.
European Patent 0 599 096 A1 (to Michelin; Jun. 1, 1994) describes the preparation of solid neodymium octoate by a precipitation reaction in water from NdCI.sub.3 and sodium octoate at 90.degree. C. No information is provided on the consistency of the material.
Most of the literature deals with the preparation of Rare Earth carboxylates with ligands other than 2-ethylhexanoic, neodecanoic, versatic and naphthenic acid. The synthesis of scandium laureate, palmitate, stearate (from ScCI.sub.3 and NaOOCR in ethanol) and the synthesis of cerium (III) octanoate (from Ce(NO.sub.3).sub.3 and octanoic acid in water) is reported along with spectroscopic and physical data (from: GMELIN Handbook, Rare Earths Main Vol. D 5).
It is an object of the present invention to provide means for the preparation of solid powdery carboxylates of neodymium 2-ethylhexanoate, neodecanoate, versatate and naphthenate with emphasis on techniques promoting the powdery consistency of these products.